Past inventions have described a new class of sensor for non-contact measurement of distance (U.S. Pat. No. 6,489,917 to Geisheimer et al.). These sensors typically comprise microwave and signal processing electronics connected to a probe via a cable. The probe contains an antenna for radiating a microwave signal to an object being measured. Since there are no electronics or active elements or coils in the probe, the systems can use high temperature construction and are well suited for monitoring in high temperature environments. Gas turbine engines provide some of the hottest environments for temperature measurement. This class of sensors is also well suited for applications with high electromagnetic fields, such as large generators on gas turbines or hydroelectric dams.
In rotating machinery, the microwave sensors would normally measure the distance between the case and the rotor, or in a bladed rotor case the individual blades. The rotor orbit is often not circular and contains some amount of rotordynamics that cause the rotors to move eccentrically. To accurately characterize the motion, at least two probes are positioned 90 degrees apart from one another to measure the two-dimensional motion. In more complex situations, the case into which the sensor is mounted may deform into an oval or tri-lobe shape that can affect the distances between the rotor and the case. To accurately characterize these conditions, additional sensors may be needed, up to eight or more per stage to be monitored. If multiple stages are to be measured the number of probes can exceed 64 or more.
In many situations, it is not necessary to continuously record data from all of the probes at the same time. Also, current embodiments of sensor systems need one electronics card for every probe to be measured. The large number of cards can take up a large amount of space and power. Therefore, it is desirable to have a technique that could reduce the number of electronics cards in the system while still being able to collect the necessary data to accurately characterize the rotating machinery. Also, in applications such as monitoring aircraft engines, weight is a significant concern. Therefore, any method that decreases the weight of the overall system while providing the same monitoring benefits is advantageous to the user.
In view of the foregoing, it will be appreciated that the application of multiple sensors for measuring rotating machinery requires a different approach than that found in the prior art. Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.